Yellow Flag Iris

Fact SheetIris pseudacorus

Images of this species:

Common look-alikes:



Iris pseudacorus is a herbaceous perennial that can grow up to 3-4 feet in height.


Broad, sword-shaped leaves are stiff, erect and glaucous. They measure between 1.6-3.3 feet long and 0.4-1.2 inches wide. Rhizomes are pink-fleshed and 0.4-1.6 inches in diameter.


Flowers are showy and bloom from April to June. Usually yellow, their color can range from nearly white to cream. Flowers are 2.75-3.5 inches wide. They are borne on erect peduncles with several flowers per stem. There are six perianth clawed segments. Three of these are upward-pointing petals and three are down-ward spreading sepals. Sepals often have purple, brown or red veins on their yellow surface.


Fruits are 1.6-2.7 inches long capsules. The capsules are 6-angled and cylindric-prismatic to ellipsoid. The average capsule contains about 120 white seeds that harden and turn brown as they mature.


This species is Quarantined: Class B Noxious Weed

This is considered a watch list species


Native to Europe


Floodplain Forest, Lake or Pond, River or Stream, Yard or Garden. Iris pseudacorus can be found along the edges of lakes, ponds, rivers and streams and immersed in water up to 10 in. deep. It grows well in freshwater wetlands and can tolerate high acidity. In its native habitat, Iris pseudacorus can tolerate living in the upper zones of salt marshes, where it may be surrounded by saline water. The plant also tends not to favor calcareous substrates, though there are exceptions to this, such as along the Housatonic River of Connecticut.

Life cycle

The showy flowers of Iris pseudacorus bloom from April to June. The fruits are 1.6-2.7 in. long capsules. These capsules are 6-angled and cylindric-prismatic to ellipsoid in shape. The average capsule contains around 120 seeds that start out white, then harden and turn brown as the season goes on.

Ecological Threat

Iris pseudacorus forms large clonal populations that displace native species. The rhizomes of this plant are able to survive rather heavy droughts. Both the rhizomes and seeds of this plant can be transported downstream, allowing for further spread of the plant. The seeds of Iris pseudacorus can germinate even after a wetland area burns. In its native habitat, this plant is not widely grazed because of the glycosides it contains, making it poisonous to grazing animals. No birds are known to disperse the seeds of this plant. Iris pseudacorus is still sold and used for water gardens. Caution should be used when hand-pulling this plant, as it can cause skin irritation.

Management Options

CAUTION! This plant contains toxins that cause minor skin irritation.

Wear appropriate clothing to prevent resinous substances from contacting skin.

Mechanical Control

Caution should be used if pulling out this plant because it can cause skin irritation; remove seed pods to help control population expansion; dig up small infestations; remove entire rhizome root system; use chopping machines for larger infestations; burn where conditions allow.

Chemical Control

  • Be careful not to damage or kill nearby native plants when conducting management work.

  • Always read and follow pesticide label directions. Application of pesticides may require a certification from the Agency of Agriculture, Food and Markets. The Agency website provides information on what applicator certification is needed.

It can be effectively controlled using any of several readily available general use herbicides such as glyphosate that is approved for wetland habitats.


Photo Credit

5387429, Joseph M. DiTomaso, University of California - Davis,

5207011, 5207008, Nancy Loewenstein, Auburn University,

5454510, Elmer Verhasselt,

Information Credit 

Invasive Plant Atlas of New England

USDA Forest Service